The present invention relates to apparatus and a method for installing a starter-generator on an aircraft engine.
Starter-generators installed on aircraft engines weigh from 30 to 50 lbs. and are usually installed by one aircraft mechanic. Often, the generator installation has to be made under an engine, while the mechanic is in a crouching position. At other times, the installation is made 10 to 12 feet above the ground, while the mechanic is standing on a workstand. Handling a 30 to 50 lb. starter-generator then becomes hazardous to the mechanic and costly if the starter-generator, which costs $4,000 to $10,000, is dropped.
The main problem is the design of the parts that are used to attach the starter-generator to the engine. From the 1940's to the 1960's, units like a starter-generator were bolted directly to the engine. The engine mounting pad had threaded studs. The starter-generator had holes in its mounting pad, which accommodated the studs and was secured by nuts coupled or screwed onto the studs.
It is very difficult to work on or provide maintenance services for most aircraft, since there is very little room between components mounted on the engine. In many cases, the mechanic cannot see, but must feel, where the nuts are to be mounted on the studs. In these cases, getting a wrench on to the nuts is almost impossible.
The aircraft manufacturers, aircraft operators, the Army, Air Force and Navy have requested an easier way to install the aforedescribed heavy starter-generators. Based on existing AN standards and MS drawings, the housing of the invention was developed that is permanently bolted to the engine drive pad. The generator is also permanently equipped with a special housing on the drive end. The engine mounted housing is called a Quick Attach-Detach, or QAD housing.
In mounting the starter-generator with the special housing, said starter-generator is inserted into the housing that was mounted on the engine. A round circular V clamp is inserted around both housings and clamps these housings tightly together, by a mechanical clamp latch. A bolt and nut on the clamp latch is tightened to pull the clamp tight around the generator and thereby locks the latch. In order to change this starter-generator, the mechanic must remove the clamp and remove the generator from the engine QAD housing.
The interface between the starter-generator mounting housing and the engine housing has a very short length of engagement. This dimension is 0.370 in. The length of engagement is purposely made short in order to make insertion of the generator into the engine QAD housing easy, since the clearance between the diameters of the two housings is 0.004 to 0.007 in., which is relatively tight.
The basic problem that existed heretofore is that, in almost all cases, one mechanic is assigned to install the starter-generator. The installation procedure is as follows:
1. The mechanic puts the loose clamp loosely around the starter-generator. PA1 2. The mechanic inserts the starter-generator into the QAD housing. PA1 3. The clamp must be positioned over the generator drive end housing and the QAD housing. This requires two hands, so the mechanic removes his hands from the starter-generator and leaves said starter-generator hanging in the QAD housing. PA1 4. The clamp must be then latched together. This also requires two hands. PA1 5. The mechanic uses a wrench to tighten the nut on the clamp.
During Steps 3 and 4 of the procedure, the pressure to hold the starter-generator in the QAD housing is lost, since both hands of the mechanic are on the clamp. Thus, the mechanic's hands are not holding the generator firmly in the QAD housing.
Very often, during Steps 4 and 5 of the procedure, the starter-generator partially backs its way out of the QAD housing and hangs partially out of the QAD housing. Thus, the starter-generator is then clamped in that cocked position. MIL-G-6162 of the military specification covering the design of the starter-generator, mandates that the drive shaft of the starter-generator be able to move radially. Most generators can move a maximum of 0.150 in.
The axial alignment of the generator is considerably off, however. Thus, when the starter-generator drive shaft rotates, in effect it is whipping. This whipping sets up a large vibration in the starter-generator, which rotates at 12,000 rpm. This vibration causes the generator carbon brushes at the rear, or anti-drive end, to bounce up and down and eventually break, causing the starter-generator to fail electrically. This vibration also causes the rear bearing to fail, which again results in a massive mechanical failure of the starter-generator.
The results of starter-generator failure could readily be disastrous. If the aircraft has a single engine and the starter-generator fails at night, the battery will go dead in about 15 to 20 minutes. If that happens, it is impossible for the aircraft to land safely and it will most certainly crash. During the day, the situation is somewhat less hazardous, since the aircraft may be able to land on a road. If the aircraft is a twin-engine aircraft, then operating on one generator is also dangerous, since part of the electrical load on the aircraft must be shut down. This is considered an emergency procedure by the Federal Aviation Administration and the aircraft also has to land quickly, before the battery goes dead. If it is a military aircraft, the mission would have to be cancelled.
The principal object of the invention is to provide an apparatus and method for installing a starter-generator on an aircraft engine coaxially and with structural integrity.
An object of the invention is to provide an apparatus and method for installing a starter-generator on an aircraft engine in a manner whereby the starter-generator will not fail due to vibration or mechanical failure.
Another object of the invention is to provide an apparatus and method for installing a starter-generator on an aircraft engine with minimal hazard to the installer.
Still another object of the invention is to provide an apparatus and method for installing a starter-generator on an aircraft engine with little danger of damage to the starter-generator.
Yet another object of the invention is to provide a method for installing a starter-generator on an aircraft engine which leaves the installer's hands free after each step so that he may maintain the coaxial and structural integrity of the coupling of the starter-generator and the engine to each other.
Another object of the invention is to provide apparatus for installing a starter-generator on an aircraft engine with coaxial and structural integrity.
Still another object of the invention is provide apparatus and a method for installing a starter-generator on an aircraft engine with less difficulty than heretofore and with considerably greater efficiency, effectiveness and reliability.
Yet another object of the invention is to provide an apparatus and method for installation of a starter-generator on an aircraft engine by only one person with minimum hazard to the installer.